1. Field of the Invention
The invention relates to a method and system wherein the fluid stream from an object to be evacuated is filtered before it enters into a vacuum pump with maximum purity of 99% and up to a particle size of 0.3 microns with a minimum pressure difference, thereby improving the life cycle of pump and process performance of the system.
2. Description of Related Art
A vacuum is a negative pressure condition created to remove gas molecules from a process work chamber with the object of providing a clean work space free of gases that effect product quality and process performance. Vacuums are is used in numerous industrial products, processes and applications like lighting products, drying of chemicals, vacuum conveying systems, electronic industry, semiconductor processes, food and pharmaceutical processes, reactors, picture tube manufacturing processes etc. To evacuate the process chambers different kinds of vacuum pumps are used depending on vacuum level.
Vacuum pumps are divided mainly in four major categories as under
a) Rough Vacuum—760 to 1 Torr (typical pumps used are roots, screw diaphragm and claw pumps among others)
b) Medium Vacuum—1 to 0.001 Torr (typical pumps used are oil sealed and piston type pumps)
c) High Vacuum—0.001 to 10 sup(−7) torr (typical pumps used are diffusion and turbo molecular pumps)
d) Ultra High Vacuum—pumps used for less than 10 Sup (−7) torr.
The above vacuum pumps are used to evacuate all work chambers/objects in order to get desired results for product, process & performance as per process requirements.
In this process of evacuation there are always chances that small quantities of dust, mist, chemical fumes or foreign materials will enter the vacuum pump's chamber thereby increasing the chances of wear and tear of all moving parts of pumps. These foreign materials will contaminate the pumps; oil and water and thereby reduce their efficiency and efficacy enormously. Oil ring vacuum pumps therefore require periodic oil replacements to maintain pump performance. If the foreign particle size is, then these same particles will not only have an impact on the mechanical performance of all moving parts in all types of pumps, but would also increase the maintenance cost of pump due to wear and tear of all moving parts and would also increase power cost. If oil is contaminated the vacuum pump's performance will come down drastically and it would fail to serve its intended purpose.
In some processes where the contamination from the process is high, users generally go for water ring vacuum pumps as these impurities from process will mix with sealing water and then would be discharged out along with water. However these water ring vacuum pumps would generally consume more power and delivers lesser vacuum as compared to oil ring vacuum pumps and would also generates lot of water effluent.
To avoid the problems of impurities in vacuum pumps now a days dry/screw type vacuum pumps have been developed which can generate 0.1 torr with additional booster pumps and are available in markets but are quite expensive. Screw type vacuum pumps also have limitations about dust load. In such cases also periodic cleanings are needed as explained in US Patent Application No. 20070172361.
Other than this if dangerous chemicals or other non environment friendly foreign materials enter into the oil there will be problems with disposal of oil when contaminants endanger to the environment and society. When such oil is disposed it may effect the environment very badly if the disposed oil is not handled properly or recycled properly.
Water ring vacuum pumps can take ample amounts of dust and fumes load from process effectively as compared to oil ring/dry screw/claw type vacuum pumps. Water ring vacuum pumps however consume more power and an auxiliary water pump is required to feed the water in to vacuum pump and finally water ring vacuum pumps will deliver less vacuum than that by oil ring vacuum pumps. Over and above this the water also required to be get cooled in cooling towers and handling this contaminated water is an issue especially where contamination is high. If the water is not handled or treated properly the quality of the water will effect the environment.
There are steam ejector type vacuum pumps also available which can deliver up to 0.1 Torr with two or more pumps in series arrangement. However, these pumps require a lot of heat to generate steam and again the steam contaminated with foreign materials produce bad quality steam condensate and this will increase the hardness of water. If same condensate is re-circulated through the boiler it leads to lot of scaling and further contributes to the reduction in thermal efficiency of the boilers.
To filter the fluid stream there are some mechanical filters which are in use at present. There are the following likely drawbacks to using the same filters on vacuum pump suction lines.
a) Heavy pressure drops and therefore the vacuum pressure difference is more.
b) High conductance drops
c) Frequent chocking/replacements of filters.
d) Increase of cycle times
e) Reduction in ultimate vacuum level
f) Indication for filter choking is very difficult and therefore expensive.
g) Ordinary mechanical filters can't filter the oil, mist effectively,
h) Mechanical filters can work up to 5 microns effectively.
There are lot of different types of traps to trap liquid fumes entry in to vacuum pumps like refrigerant traps, liquid nitrogen traps etc. These are very expensive and have high operating costs.
Normally in the wine processing industry the air stream towards the vacuum pump is heated up to 110° C. to kill the bacteria which is going out from the vacuum pump. Otherwise all bacteria will go out and effect the environment badly. In this process of heating a lot of electrical energy is needed to heat the air flow.
Diffusions pumps are made available for vacuum levels up to 1×10 sup (−10) torr for high vacuum applications. These pumps face the problem of oil back streaming into the process chamber or product to be evacuated. This back streaming of oil in PPM (Parts per Million) levels will effect process performance and/or product quality very badly. The same are discussed in detail in U.S. Pat. No. 3,782,816 and U.S. Pat. No. 5,700,134.
In any process of productions where steps involves reactions, melting, crystallizations, coatings, filling, drying, fermentation in a vessel for further processing a particular pressure is necessarily required to be carried out in vacuum. Thus the specific gravity of gas which flows into the vacuum pump is very small. When the gas together with other constituents flows into the vacuum pump, the gas flows appropriately but the crystallization in the vessel for processing prevent the reaction or reduced ability to convey other constituents which includes substantially the dust particles and therefore dust is accumulated in the vacuum pump. There are several inventions, which deal with this difficulty and have been able to reduce the amount of accumulated dust but how ever could not facilitate the satisfactory running of the vacuum pump and thereby require frequent operations to remove the dust in the vacuum pump.
To prevent dust from flowing into vacuum pumps attempts have been made to separate the dust by providing filters/cyclone separators, traps and traps in series or the like between the vacuum pump and the dust producing device however there was not a complete solution because dust causes blocking of through-parts in the filter, the efficiency of which are then greatly reduced. The effective evacuation performance of the vacuum pump for the process of production by reaction, melting and crystallization vessel for processing prevents the reaction process, the melting process and the crystallization process on a continuous basis.
For any process performances which are to be performed in vacuum, their efficiency/effectiveness, productivity and product quality is are dependent on the vacuum level achieved in any such process. If foreign materials, fumes and dust and mist enters in vacuum pump it will reduce vacuum level and same will effect over all performance of the process. If dust enters into any vacuum pump in the middle of the process cycle, the pumping capacity of vacuum pump will come down and this will increase the cycle time or reduce process performance.
Vacuum pump pumping capacity depends on conductance of pipe lines and restrictions, if any. For example if the vacuum pump has a capacity of 100 Liters per minute (LPM) and if there is a restriction in pipe line the vacuum pump would conduct only 90 Liters per minute (LPM) the net pumping capacity of said vacuum pump would thus be restricted to 90 Liters per minute (LPM). On account of this problem people will not prefer to install any kind of mechanical filters where process vacuum is more important than maintenance of vacuum pumps.
To work in a dusty/fumes environment, process of evacuation suitable pumps are water jet/water ring/steam jet (single stage/multiple stage) vacuum pumps; these pumps can take the load of impurities from process but the draw back in these systems are:
I) Inefficient compared to other systems oil ring screw type vacuum pumps.
II) Generates low vacuum levels than oil ring vacuum pumps
III) Generates lot of effluent because mixing of fumes/dust in sealing fluid stream (sealing fluid is steam in case of steam jet vacuum pumps and water in case of water ring and water jet vacuum pumps).
IV) Consume more electric power.
V) Consumes more steam.
Various other improvement have been suggested such as:
U.S. Pat. No. 5,776,216: A vacuum pump filter for filtering debris from a semiconductor(s) system is disclosed. The vacuum pump filter includes an inlet port for connecting to a chamber. A first filter holder is connected to the inlet port for filtering large debris. A second filter holder for filtering middle debris is connected to the first filter holder. A third filter holder is connected to the second filter holder for filtering small debris. A outlet port is connected to the third filter holder via a terminal. The other terminal of the outlet port is connected to a pump system.
United States Patent Application #: 20060276049
Title: High efficiency trap for deposition process
Abstract: The present invention provides a system, apparatus and method for improving the efficiency of a semiconductor(s) processing system, such as a deposition system by decreasing or substantially eliminating the accumulation of by-products in the apparatus components of the semiconductor(s) processing system. The present invention further relates to improving the efficiency of a fore line trap associated with a semiconductor(s) processing system, wherein the trap removes substantially all of the by-products from the exhaust gas from the processing chamber. In addition, the present invention provides a system, apparatus and method for efficiently clearing traps of accumulated by-products from exhaust gas of a semiconductor(s) processing system.
Device and method to mitigate hydrogen explosions in vacuum furnaces
U.S. Pat. No. 6,888,713
Abstract:
A device to mitigate hydrogen explosions in a vacuum furnace includes at least one igniter, an ignition transformer, and an electrical switch. The at least one igniter includes a set of high-voltage Electrode(s)s and is connected to the ignition transformer by high-voltage wires. The electrical switch activates the ignition transformer to provide power to the at least one igniter forming a continuous electrical arc between the Electrode(s)s. The at least one igniter is located inside the vacuum furnace at an opening where air may enter the vacuum furnace, which may contain a hydrogen and steam gas mixture under accident conditions. The device consumes hydrogen by controlled combustion as flammable mixtures are formed.
United States Patent Application #: 20070231162
Title: Vacuum pump
Abstract: A multi-stage vacuum pump comprises, between adjacent stages of the pump, a continuous ignition source for igniting a fuel within a pumped fluid. This can ensure that the concentration of the fuel in fluid exhaust from the pump is below its lower explosive limit.
United States Patent Application #: 20070201988
Title: Vacuum pump
Abstract: A vacuum pump comprises a rotor assembly mounted on a driven shaft, and a motor for rotating a drive shaft in forward and reverse directions. A driven member is located on the driven shaft and a drive member is located on the drive shaft for engaging the driven member to couple the driven shaft to the drive shaft. Each member has first and second impact surfaces. The members are configured to permit at least one quarter of a revolution of the drive member relative to the driven member in either the forward or the reverse direction before one of the impact surfaces of the drive member impacts upon a corresponding impact surface of the driven member. This can enable the drive member to acquire sufficient angular momentum before it impacts the driven member such that the amount of energy transferred to the driven shaft upon impact can be sufficient to free a pump that has become locked by process deposits. In the event that the pump is not restarted “first time”, the motor direction can be reversed to bring the other impact surfaces into contact with the same angular momentum. This sequence can be repeated as required until the pump restarts.
United States Patent Application #: 20060228272
Title: Purifier
Abstract: A purifier is described for use in a gas processing application. The purifier comprises a chamber having a gas inlet and a gas outlet. A series of baffles are arranged in the chamber and coated with a getter material selected for its ability to react with species to be removed from a gas stream and form stable compounds. The chamber also houses a source of the getter material, which is periodically activated to refresh the coating of getter material on the baffles.
U.S. Pat. No. 3,782,861
Abstract: An oil diffusion pump which has a plurality of coaxially arranged cylindrical chimneys extending from the bottom of a cylindrical envelope. The bottom of said envelope has hollow projections extending upwardly between the chimneys and a heating element has portions thereof extending into said hollow projections.
U.S. Pat. No. 5,700,134—Diffusion pumps
Abstract: A diffusion pump is provided with an outer body and a chimney positioned within the outer body. A top cap is positioned about the top of the chimney to form an annular passageway (or an annular array of passageways) there between. A guard ring is positioned generally above the top cap. Coolers cool the outer body and the guard ring and working fluid present in the base of the outer body is heated to cause evaporated oil to pass up the chimney. A baffle, substantially thermally isolated from the guard ring, is contained within the outer body.
U.S. Pat. No. 2,377,391 (1945) to White discloses one of the earliest inventions regarding electronic air cleaners. A method and apparatus of charging suspended particles in air is taught. Once charged, a separate precipitator removes the particles. Broadly speaking, the invention comprises increasing the strength of the electric field between a discharge and a non-discharge Electrode(s) in the portion of the field adjacent the non-discharge Electrode(s). This may advantageously be effected by providing a previous, non-discharging auxiliary or grid Electrode(s) member between the discharge Electrode(s) and non-discharge Electrode(s), and maintaining a substantially greater potential difference per unit of spacing between the auxiliary Electrode(s) and non-discharge Electrode(s) than between the discharge Electrode(s) and the auxiliary Electrode(s). The auxiliary Electrode(s) is maintained at a potential between that of the discharge Electrode(s) and that of the non-discharge Electrode(s), so that the polarity of the field between the discharge Electrode(s) and the auxiliary Electrode(s) is the same as that of the field between the auxiliary Electrode(s) and the non-discharge Electrode(s).
U.S. Pat. No. 3,915,672 (1975) to Penney discloses an electrostatic precipitator having parallel-grounded plate Electrode(s) dust collectors. High voltage corona wires are located between the plate Electrode(s)s. They charge the dust particles, which are then drawn to the plate Electrode(s)s. The corona wires are pulsed in order to prevent back-corona which otherwise occurs due to the high resistivity of the dust accumulation on the plate Electrode(s)s.
U.S. Pat. No. 5,055,118 (1991) to Nagoshi et al. discloses an electrostatic dust collector. A first positive ionization Electrode(s) positively ionizes the dust. Then the dust passes into a chamber having a pair of un-insulated Electrode(s)s at a high voltage, separated by an insulation layer. Coulomb's law causes the dust to collect on the grounded Electrode(s), thereby neutralizing the charge of the dust particles. The dust only collects on the grounded Electrode(s) due to special gaps in the laminate, which prevents dust build-up on other components. The theory is that dust accumulation on only the grounded Electrode (s) does not cause significant deterioration of the electric charge due to the neutralization by the dust particles. However, it is clear that cleaning of the negative Electrode(s)s is necessary to maintain airflow.